(1) Field of the Invention
The present invention relates generally to combustion monitoring systems and, more particularly, to an apparatus for precisely monitoring the unburned carbon and other combustibles, such as hydrogen and sulfur, content produced by a fossil-fueled boiler.
(2) Description of the Prior Art
Loss on Ignition (LOI) measurements are becoming increasingly important for utility coal fired plants for several reasons. For example, the low NOx burners that are being installed by a large percentage of coal fired plants produce higher LOI than the burners being replaced, even when the new burners are optimally tuned, and excessive amounts when the burners are poorly tuned. If the LOI of the fly ash increases, the plant must burn more coal to produce the same power (degrading plant heat rate). In addition, the higher carbon content fly ash may not be salable for use as building material, loadings on the bottom ash and fly ash systems will increase, and stack opacity may increase. Accordingly, it has become important to obtain reliable and timely mass flow of unburned carbon and other combustibles content (M.sub.UBC) measurements.
Most plants currently determine LOI by extracting an ash sample from the precipitator or baghouse hoppers or by isokinetic samples located, typically, downstream of the air heater and then use an ASTM procedure (% weight loss) to determine the unburned carbon and other combustibles content. Typically, this determination is performed once a day. The ASTM procedure takes about 4 hours to complete. Since real time information is not currently available, burner tuning and control to balance emissions (NOx) and efficiency (LOI) is very difficult at best.
There have been several attempts to provide an automatic LOI system on the market. These systems attempt to automatically extract an ash sample from the boiler and conduct the ASTM procedure on-line to produce a semi-real time indication. However, these systems have generally been unreliable and expensive due to mechanical problems associated with extracting hot and abrasive particles from a boiler. Specifically, the ash lines clog and corrode due to heat. Also, there is the question of whether a single measurement which, at best, produces only a single point value rather than a real time measurement is representative or not.
Thus, there remains a need for a new and improved M.sub.UBC, monitor which is operable to provide a real time indication of fly ash LOI.